Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus using the same, and particularly to a zoom lens that is most appropriate for cameras such as a video camera, a digital camera, a TV (television) camera, and a surveillance camera.
Description of the Related Art
There are various image pickup apparatuses such as a video camera, a digital camera, a TV camera, and a surveillance camera. These image pickup apparatuses are sought to have a small size, a capability to capture an image with a high image quality, and an optical system having a high zooming.
As a zoom lens suitable for such image pickup apparatuses, a zoom lens that includes four lens units is available. For instance, as a four-unit zoom lens, a zoom lens which includes in order from an object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power, has hitherto been known.
In this four-unit zoom lens, at the time of zooming from a wide angle end to a telephoto end, the first lens unit and the third lens unit are fixed, and the second lens unit and the fourth lens unit move. The zooming is primarily carried out by moving the second lens unit from the object side to an image side, and a fluctuation in an image plane that occurs due to the movement of the second lens unit is corrected by moving the fourth lens unit. Moreover, the focusing is carried out by moving the fourth lens unit in an optical axial direction.
In recent years, as an image to be used in a field of broadcasting, an image having a high resolution (an image having a high-definition) has been sought. For acquiring such image, an image pickup element with a large number of pixels has been adopted in broadcast equipment. A zoom lens is also required be compatible with such broadcast equipment. For this, the zoom lens is sought to have a high resolving power. Moreover, in order that photography at even darker location becomes possible, the zoom lens is sought to have a small F-number.
As a zoom lens having a comparatively higher resolving power and a comparatively smaller F-number, zoom lenses in Japanese Patent Publication No. 4695912, Japanese Patent Publication No. 5028104, Japanese Patent Publication No. 5318262, Japanese Patent Application Laid-open Publication No. 2013-050519, and Japanese Patent Application Laid-open Publication No. 2013-117656 have been known. These zoom lenses include in order from an object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power.
In the zoom lens according to Japanese Patent Publication No. 4695912, at the time of zooming, the first lens unit and the third lens unit are fixed, and the second lens unit and the fourth lens unit move. The first lens unit includes one cemented lens and one single lens.
In the zoom lens according to Japanese Patent Publication No. 5028104, at the time of zooming, the first lens unit and the third lens unit are fixed, and the second lens unit and the fourth lens unit move. The first lens unit includes either, one cemented lens and one single lens, or includes one cemented lens.
In the zoom lens according to Japanese Patent Publication No. 5318262, at the time of zooming, the first lens unit and the third lens unit are fixed, and the second lens unit and the fourth lens unit move. The first lens unit includes either, one cemented lens and one single lens, or includes one cemented lens, or includes one single lens.
In the zoom lens according to Japanese Patent Application Laid-open Publication No. 2013-050519 and Japanese Patent Application Laid-open Publication No. 2013-117656, at the time of zooming, the first lens unit and the third lens unit are fixed, and the second lens unit and the fourth lens unit move. The first lens unit includes one cemented lens and two single lenses.